This invention deals generally with heat transfer from a high power density surface, and more specifically with a structure for cooling such a surface by means of a porous layer through which liquid or gas is pumped.
Cooling a high power density surface, that is, a surface to which intense heat is being delivered, is a particularly difficult problem. If the heat is delivered to the surface in multiple locations, or generally across the entire surface, the heat removal must similarly be over the entire surface. In the simplest configurations, such as with liquid flowing through cooling pipes attached to the backside of the heated surface, just the thermal resistance through the heated surface between the heat input point and the heat removal pipe can permit the surface temperature to rise too high.
Even with the use of evaporation cooling it is difficult to accomplish reliable cooling of such a surface. One reason is that high heat input at one location can create a high vapor pressure at that point and prevent additional liquid from reaching that location for generation of additional cooling vapor. Such a situation can lead to destruction of the surface.
Although there have been some approaches to cooling a heated surface without the use of evaporation, they also have not proven entirely satisfactory. U.S. Pat. No. 5,727,618 by Mundinger et al suggests one typical approach for cooling a high power density surface of a laser diode array. That patent discloses channels in a solid plate adjacent to the heated surface. U.S. Pat. No. 5,205,353 by Willemsen et al discloses alternating complimentary wedge shaped channels formed in a porous layer, with fluid fed into every other channel and out the channels between the input channels.
Such channeled designs suffer from several shortcomings. Those with solid channels such as Mundinger et al are easier to manufacture, but only directly cool the portions of the heated surface in contact with the fluid channels. The balance of the heated surface must conduct heat through the heated structure to reach the portions in contact with the fluid in the same manner as is required for attached pipes.
Those designs, such as Willemsen et al, which have channels in porous materials, are difficult and expensive to manufacture. Furthermore, they only supply a limited quantity of additional fluid in contact with the heated surface. They only add the cooling fluid flowing through the portion of the porous layer in direct contact with the heated surface to the amount which would be supplied by channels in adjacent solid material. Fluid passing through the porous material only a small distance removed from the heated surface adds little to the heat transfer from the heated surface.
It would be very advantageous to have a cooler which supplied fluid to the entire heated surface and yet was simple to manufacture.